Photodetectors include, for example, a photodetector using quantum wells or quantum dots, that is, a quantum photodetector. Such a quantum photodetector includes, for example, a quantum infrared detector.
A photodetector using quantum dots among these photodetectors is configured such that electrons bound to quantum dots absorb light, are excited, escape from the bound state, and generate optical current. For example, Japanese Laid-open Patent Publication No. 2015-88688, Japanese Laid-open Patent Publication No. 2001-44486, and the like are disclosed as related arts.
For the photodetector using quantum dots, quantum dots having a desired size and quantum levels leading to a desired detection wavelength are desirably formed.
However, despite the intention to form the quantum dots having the desired size and the quantum levels leading to the desired detection wavelength, the size variation in the quantum dots causes formation of quantum dots of sizes other than the desired size.
The quantum dots of the sizes other than the desired size have different quantum levels. Accordingly, the quantum dots do not contribute to optical current but contribute to dark current (noise current).
For example, quantum dots of a size larger than the desired size do not contribute to optical current due to an absorption probability decrease, a decrease in excited level escape probability, or the like but contribute to dark current due to trapping of electrons flowing as the optical current, electron escape caused by thermal excitation, or the like.
For example, quantum dots of a size smaller than the desired size do not contribute to optical current due to an absorption probability decrease, a transition probability decrease, or the like but contribute to dark current due to trapping of electrons flowing as the optical current, electron escape caused by thermal excitation, or the like.
As a result, a signal-to-noise ratio (S/N) of the photodetector is deteriorated.
Under these circumstances, an S/N is desirably improved in a photodetector using quantum dots.